In accordance with recent westernization in the lifestyle, ischemic heart diseases (including angina pectoris and cardiac infarction) are rapidly increasing in Japan. An ischemic heart disease is caused principally when coronary thrombosis or coronary twitch is caused additionally to an arteriosclerotic disease of a thick coronary artery extending on the heart surface.
As a treatment method for angiostenosis, angioplasty (PTA, PTCA or the like) in which a small balloon is expanded within a blood vessel for the treatment is widely employed as a minimally invasive treatment. In employing this treatment method, however, stenosis (restenosis) is repeatedly caused in high probability. As a method for reducing the ratio of the restenosis, a stent placement technique is being rapidly spreading these days.
Since a stent is used to be indwelled in a body, it is required to have durability against biological materials and compatibility with an organism. As a method for providing a medical material such as a stent with durability, a method in which the surface of the medical material is coated with a diamond-like carbon film (a DLC film) is known (see, for example, Patent Document 1). Since a DLC film is a very smooth and chemically inert film, it is characterized by being minimally reactive with biogenic components. Accordingly, when the surface of a base material of a stent is coated with a DLC film, a stent with high durability and good biocompatibility can be obtained.
On the other hand, it has been reported that the restenosis occurs at frequency of approximately 20% through 30% also in employing the stent indwelling technique. In the case where the restenosis occurs, it is necessary to perform the PTCA again, and it is a global problem of great urgency to establish methods for preventing and treating the restenosis.
As a method for preventing the restenosis, an attempt has been made to coat the base material of a stent with a drug for restricting the occurrence of occlusion. For example, Patent Document 2 discloses a method for coating a stent by spraying a polymer solution including a drug over the surface of the stent or by immersing the stent in the polymer solution. Thus, a stent from which an anti-restenosis drug is gradually released can be realized.
Patent Document 1: Japanese Laid-Open Patent Publication No. 10-248923
Patent Document 2: National Publication of Translated Version No. 2005-531332
Patent Document 3: National Publication of Translated Version No. 2002-517285